I also have WIN (had them fitted 2 months ago,) and it's awesome that you feel okay so far.
From my experience the first 2 weeks after having the linguals fitted are the worst, (though I did have both sets put in at once,) but it's just as possible that you might be one of the lucky ones and have very little discomfort at all. However if you do start to get a few tongue ulcers or whatever - I often find my teeth start to ache on a time lag of about a day after I have an appointment - don't panic, as it is definitely all temporary.
But to your question - for me, the top set was the worst for lisping. Not to be pessimistic, but you will still probably have quite a lisp 2 days after having them put in. The top set I found was also the worst for tooth pain, (even now my front 2 teeth are more sensitive than they used to be.) The bottom set I found tore up my tongue the most - but if you haven't gotten many ulcers yet, maybe that won't be the case for you.
From reading the forums and people's blogs I've found that linguals seem to be a very personal experience for everyone - for example I got very bad tooth pain for at least the first month and had to live off of liquid foods for quite a while - whereas some people were back to eating steak and chips 3 days in!
I think that getting each set of linguals separately was a smart idea though, and I hope that it does continue to not be too hard for you!
